X-ray tube

Abstract

An X-ray tube 1 includes spacer 8 which is cylindrical so it does not block electrons 80 directed from a grid electrode 72 toward a focusing electrode 25 , and which has one end 8 b fixed to the grid electrode 72 and the other end 8c abutting against the focusing electrode 25 . The distance between the grid electrode 72 and focusing electrode 25 is set to a predetermined distance by the spacer 8.

What is claimed is:  
     
       1. An x-ray tube comprising: 
       a housing;  
       an electron gun provided proximal a grid electrode in said housing;  
       a focusing electrode integrally formed in said housing;  
       a spacer having a distal end abutting against said focusing electrode and a proximal end fixed to said grid electrode, said spacer having a predetermined structure allowing electrons directed from said grid electrode toward said focusing electrode to pass through said predetermined structure, wherein said spacer precisely maintains the distance between said focusing electrode and said grid electrode, and said spacer has a hole in a circumferential wall thereof through which an inside and an outside of said spacer communicate with each other; and  
       a stem supporting said electron gun on at least one stem pin, said housing being sealed by said stem.  
     
     
       2. An x-ray tube comprising: 
       a housing;  
       an electron gun provided proximal a grid electrode in said housing;  
       a focusing electrode integrally formed in said housing;  
       a spacer having a distal end abutting against said focusing electrode and a proximal end fixed to said grid electrode, said spacer having a predetermined structure allowing electrons directed from said grid electrode toward said focusing electrode to pass through said predetermined structure, wherein said spacer precisely maintains the distance between said focusing electrode and said grid electrode; and  
       a stem supporting said electron gun on at least one stem pin, said housing being sealed by said stem;  
       wherein said grid electrode comprises:  
       a plate-shaped base portion with an opening, at a center thereof, through which the electrons pass; and  
       a cylindrical portion which is integrally molded with said base portion from the same material as that of said base portion, is formed cylindrical so the electrons directed from said opening toward said focusing electrode can pass therethrough, and has one end abutting against said focusing electrode, characterized in that said cylindrical portion has a hole in a circumferential wall thereof through which an inside and an outside of said cylindrical portion communicate with each other.